Drill collar



Feb. 28, 1967 E. B. WILLIAMS, JR

DRILL COLLAR Filed March 16, 1965 INVENTOR fd'Wd/'a/, [4f/M0015, ./r.'

l d i l W|I Y A TTOENEY `with the wall of the bore hole.

United States Patent Gilce 3,306,373 Patented Feb. 28, 1967 This invention relates to. drill collars used in a drilling string for boring holes at substantial depths into the earth .so as to maintain a stiff stem above the drill bit when the weight of the drill pipe is applied to the bottom of the bore hole for increasing the drilling rate and without causing deviation of the bit.

Such drill collars, prior to the present invention, consist, of one or more stands that are inserted in a drilling string above the drill bit, and, being subject to weight of the drill pipe, tend to llex and corkscrew, so that the drill bit deviates from a straight course, resulting in a crooked hole.

Attempts have been made to construct the drill collars of extra heavy large diameter pipe, so as to get as much metal and weightV into them as possible for imparting the stiness necessary for resisting flexing and corkscrewing of the drill stem. However, when such drill collars lit more or less tightly in the bore hole, there is insufficient space to allow adequate circulation of the drilling fluid used to carry the cuttings to the top of the bore hole. Also, the drill collars are apt to wedge in the bore hole. When such drill collars of extra weight but smaller size are used to maintain adequate circulation of the drilling fluid, they are not sufficiently stiff to eliminate corkscrewing and deviation of the drill bit.

More recent attempts have been made to minimize deviation of the drill bit by construction of the drill collars so that a locking eifect takes place to limit the extent to which corkscrewing can take place. Such construction only minimizes deviation of the drill bit, and doesnot prevent drilling of a crooked hole. Also, the drill bit is apt to pick an angle of deviation in parts of the formation to take olf at increasing angles under the corkscrew effect imparted by the drill collars.

It is the object of the present invention to provide stands of drill collars constructed and arranged relative to each other for maintaining a straight drill stem above the bit that is backed by the wall of the bore hole, and thereby eliminate the force tending to deflect the drill bit from the vertical, while at the same time providing drill collars that remain loose in the hole Further objects of the invention are to provide drill collars that are eccentrically connected into the drilling string so that one diametrical side thereof is supported from flexing by the wall of the bore hole; and to provide the drill collars on the offset sides thereof with wear resistant ribs that are in contact with the Wall of the bore hole.

In carrying out the invention, the drill collars are provided with extra heavy cylindrical bodies preferably of larger diameter than the diameter of the drill pipe to which the cylindrical bodies are eccentrically connected by means of the tool joint connections on the ends thereof, whereby the drill collars gyrate in continuous contact Uniformity of support on the wall of the bore hole is attained by use of two or more collars arranged symmetrically about the axis of rotation, so as to maintain the support and stiffness required in maintaining linear alignment of the bit with the axis of rotation.

The improved structure is illustrated in the accompanying drawings, wherein:

FIG. l is a longitudinal section of a -bore hole being drilled by a drilling string equipped with the usual drill collars, and illustrating the corkscrew deflection that takes place under load of the drill pipe.

FIG. 2 is a similar section through a bore hole in which the drilling string includes drill collars constructed in accordance with the present invention, and showing the straight stem maintained therewith.

FIG. 3 is an enlarged view of one of the drill collars constructed in accordance with the present invention, with an intermediate portion thereof removed to shorten the ligure, the upper tool joint member of the drill collar being shown in section.

FIG. 4 is a plan View of the upper end of the drill collar shown in FIG. 3.

FIG. 5 is a cross section through the drill collar taken on the line 5-5 of FIG. 3.

FIG. 6 is an enlarged fragmentary cross section to illustrate, in better detail, the contact rib.

Referring more in detail to the drawings, and first to FIG. l:

1 designates a bore hole being drilled through earth formations by means of a rotary drill bit 2 which forms a part of a drilling string 3. The drilling string is made up of a series of stands of drill pipe 4 interconnected by the customary tool joints 5. The upper end of the drilling string is rotated by a suitable mechanism (not shown) to rotate the bit 2 and the drilling string is lowered on deepening the -bore hole to maintain the weight of the drilling string 3 on the drill bit 2. Connected into the drilling string 3 between the lowermost drill pipe 4 and drill bit 2 are a plurality of drill collars 6, connected together and into the drilling string by tool joints 7 in an attempt to maintain a stiff stem directly above the drill bit 2.

The usual drill collars 6 comprise extra heavy pipe, which may or may not be of larger diameter than the drill pipe 4, the purpose being anv attempt to provide weight and stiffness at the lower end of the drilling string, to minimize as much as possible deviation of the drill bit 2 from a vertical course. However, when the full weight of the drill pipe 4 and weight of the drill collars 6 is applied to the drill bit 2 to increase the drilling rate thereof, the drill -collars `6 are insufficient to maintain a stiff stem and they corkscrew in the bore hole 1, as shown in FIG. 1, with the result that the drill bit 2 is caused to deviate from the vertical.

It is the purpose of the present invention to avoid the difficulty as shown in FIG. 2, by providing drill collars 8 and 9 constructed and located relatively to one another so that offset portions 10 and 11 gyrate in support by the wall 12 of the bore hole 1 (FIGS. 2 and 6) to eliminate corkscrewing of the drill collars 8 and 9, and thereby maintain a stiff drill stem 13 which constitutes the drill collar portion of the drilling string 3, so as to eliminate deviation of the drill bit 2 when the full weight of the drill pipe 4 is applied thereon.

One of the drill collars of the present invention is best illustrated in FIG. 3, wherein the drill collar in-cludes a substantially solid cylindrical body 14 of larger diameter than the drill pipe 4 to impart weight and stillness into the drill stem 13. The tool joints of the drill collar comprise an internally threaded box 15 at the upper end thereof and an externally threaded pin 16 at the lower end thereof, yof the size corresponding to pins and boxes of the tool joints of the drill pipe 4. In order to provide for gyration of the cylindrical body 14, the axis 17 of the drill collar is offset from the axis 18 of the tool joint members 15 and 16. Thus the respective ends of the cylindrical body 14 are in linear alignment with each other so that when the drill collar 8 is connected into the drilling string 3, the cylindrical body 14 thereof gyrates about the rotational axis 18 which is the axis of the drill bit. The drill collar 8 is provided with a longitudinal bore 19 that continues coaxially through the box and pin 15 and 16 to provide a continuation of the drilling tluid flow duct of the drilling string. It is obvious that one diametrical side of the drill collar has a relatively thin walled portion 20, and that the opposite wall portion is substantially massive, as indicated at 21, so that that side of the body of the drill collar contains sufficient metal to provide the necessary strength, `weight and stiffness in the drill collar. Located in the medial diameter of the cylindrical body and opposite the thin side 20 (FIGS. 4, 5 and 6) is a longitudinal series of ribs 22 adapted to directly contact the wall 12 of the `bore hole during rotation of the drill collar. The ends of the ribs 22 are preferably spaced from each other as indicated at 23, and the endmost ribs terminate short of roundings ends 24 of the -cylindrical body joining with the tool joint members 15 and 16. The ribs 22 are secured to the face of the cylindrical body 14, preferably by welds 25 extending along sides there-of (FIGS. 4, and 6). Since the ribs 22 provide the bearing portions and 11 in contact with the wall 12 of the bore hole, the outer faces thereof carry parallel strips 26 of wear resistant material, such as tungsten carbide alloy, that may be suitably secured to the ribs as by welding. The outer faces of the strips 26 are curved in correspondence with the curvature of the wall yof the bore hole. The ribs 22, while contacting the wall of the bore hole, maintain a water space 27 substantially circumferentially of the drill collar, and, therefore, eliminate channeling of the drilling iiuid as it carries cuttings to the top of the bore hole. It is obvious that the cross sectional shape of the ow space 27 increases in capacity from the sides of the ribs 22 around to the opposite side of the drill collar, so that there is ample capacity for flow `of the drilling fluid.

In using the drill collars constructed as described, the pin 16 of the collar 9 is connected with the drill bit and lowered into the bore hole. The pin 16 of the collar 8 is threaded into the box 15 of the collar 9, in which position the thick wall portions 21 are diametrically opposed with respect to each other, as shown in FIG. 2, and in position to engage diametrically opposite sides of the bore hole. After lowering the drill collars into the bore hole, the stands of drill pipe are connected with the box of the upper collar and the assembly is lowered in the bore hole with the connection of each stand of drill pipe until the drill bit is bearing on the bottom of the hole.

Upon rotation yof the drilling string as in conventional practice, the portions 21 of the drill collars gyrate about the axis of the drilling string, with the wear resistant faces 26 on the ribs 22 riding in contact with the wall of the bore hole, to maintain the stem of the bit which constitutes the drill collars in concentric relation with the bore hole when the load of the drill pipe is applied to the bit to increase the drilling speed thereof. The drill pipe, under load, tends to corkscrew, however, the stem portion of the drilling string is sufficiently rigid, with the support by the walls of the bore hole, to keep the drill bit from deviating from the vertical. There is also ample space for iiow of the drilling fluid without interference by the drill collars. It is also obvious that each drill collar is loose in the hole, since it engages only side wall, so that there is no danger of a collar becoming stuck in the hole. If morethan two drill collars are coupled into the drilling string,vthe portions 21 are positioned circumferentially of the :bore hole, so that the ribs contact the wall in symmetrical relation.

What I claim and desire to secure by Letters Patent is:

1. In a rotary drilling string comprising a drill pipe and a drill bit rotated by the drill pipe for drilling a bore hole,

drill collars connecting the drill bit to the drill pipe to maintain a stiff stem above the drill bit for mini- 4 mizing deviation of the drill bit caused by corkscrew; ing of the drill pipe under load,

said drill collars each including an elongated body of less cross section than the bore hole made by the drill bit, and

means connecting the drill collars in end to end relation with major portions of the drill collars offset outwardly from the axis of rotation and with said major portion of one drill collar spaced circumferentially in symmetry with said major portion of the other to gyrate in contact with the wall of the bore hole.

2. In a rotary drilling string comprising a drill pipe and a drill bit rotated by the drill pipe to drill a bore hole,

drill collars connecting the drill bit to the drill pipe for maintaining a stiff stem above the drill bit and minimizing deviation of the drill bit caused by corkscrewing of the drill pipe under load,

each drill collar including an elongated generally cylindrical body of less diameter than the bore hole made by the drill bit, and

tool joint members eccentrically located on ends of said body for interconnecting said drill collars together with major portions of the drill collars offset outwardly from the axis of rotation and with said major portion of one drill collar spaced circumferentially in symmetry with said major portion of the other to gyrate in contact with the wall of the bore hole for stabilizing the rotational axis of the bit.

3. In a drilling string comprising a drill pipe and a drill bit rotated by the drill pipe,

drill collars connecting the drill bit to the drill pipe for maintaining a stiff stem above the drill bit to mini mize deviation of the drill bit under load of the drill pipe,

said drill collars each including an elongated cylindrical body of less diameter than the bore hole made by the drill bit,

means eccentrically connecting ends of the drill collars to each other and into the drilling string to offset major portions of said collars in circumferentially spaced apart symmetry for gyration about the axis of rotation, and

bearing ribs extending longitudinally of said portions for contact with the wall of the bore hole to retain said stem centered within the bore hole. 4. In a rotary drilling string comprising a drill pipe and a drill bit rotated by the drill pipe for drilling a bore hole through earth formations,

means for contacting the wall of the bore hole at a plurality of points circumferentially of the bore hole and at different levels to retain the rotational axis of the drill bit in the axis of the bore hole to drill a substantially straight hole,

said means comprising a plurality of elongated cylindrical body portions of larger outer diameter than the diameter of the drill pipe,

and means connecting said means into the drilling string between the drill pipe and the drill bit to provide a stiff stern for the drill bit,

said elongated cylindrical body portions being axially offset radially from the axis of rotation to provide longitudinal bearing portions in contact with the wall of the bore hole and spaced circumferentially about said axis of rotation to keep the rotational axis coaxial with the axis of the bore hole.

5. In a rotary drilling string as described in claim 4,

and in which the bearing portions comprise longitudinally spaced ribs on the offset sides of the cylindrical body portions for passing drilling fluid to reduce the amount of drilling iiuid swirled ahead of said cylindrical body portions.

6. In a rotary drilling string comprising a drill pipe and "a drill bit rotated by the drill pipe for drilling a bore hole through earth formations,

means for contacting the wall of the bore hole at a plurality of points circumferentially of the bore hole to retain the rotational axis of the drill bit in the axis of the bore hole and thereby maintain a substantially straight hole,

said means comprising drilling collars each having a cylindrical body of larger outer diameter than the diameter of the drill pipe,

tool joint members on ends of the cylindrical bodies connecting the drilling collars together and the endmost drilling collars to the drill pipe and the drill bit to provide a stii stem for the drill bit,

said axes of the cylindrical bodies being oset radially outwardly from the axis of the tool joint members to provide longitudinal bearing portions on said cylindrical body in contact with the wall of the bore hole and spaced circumferentially about said axis of rotation to keep the rotational axis of said stem coaxial with the axis of the bore hole to maintain the direction of the drill bit,

and said cylindrical bodies having bores aligning with the axis of rotation to pass the drilling Huid from the drill pipe to the drill bit and whereby the major mass of the drilling ycollars are at one side of the axis of rotation.

7. In a rotary drilling string vcomprising a drill pipe and a drill bit rotated by the drill pipe for drilling a bore hole through earth formations,

a drill collar having a cylindricalbody of larger outer diameter than the diameter of the drill pipe,

tool joint members on ends of the cylindrical body for connecting into the drilling string in providing a stifr stem for the drill bit,

said axis of the cylindrical body being offset radially 5 outwardly -from the axis of the tool joint members, longitudinally spaced apart rib members on said oiset side of the cylindrical body for bearing on the wall of the bore hole to cooperate in maintaining the direction ofthe drill bit, lo and said cylindrical body having a straight bore aligning with the axis of the tool joints to pass drilling iluid from the drill pipe to the drill bit and whereby the major mass and stiffness of the drilling 'collar is at one side of the axis of rotation.

5 References Cited by the Examiner UNITED STATES PATENTS 1,590,422 6/1926 Collier 175-398 X 20 1,954,166 4/1934 Campbell 175-399 X 2,164,348 7/1939 Ross 175-325 2,173,309 9/1939 Monroe 175-76 2,712,434 7/1955 Giles et al. 175-73 2,745,635 5/1956 Zublin 175-76 25 2,841,366 7/1958 Dunn 175-320 X 2,891,769 6/1959 Page et al. 175-76 3,180,439 4/1965 Deely 175-325 X 3,237,705 3/1966 Williams 175-406 30 CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner. 

1. IN A ROTARY DRILLING STRING COMPRISING A DRILL PIPE AND A DRILL BIT ROTATED BY THE DRILL PIPE FOR DRILLING A BORE HOLE, DRILL COLLARS CONNECTING THE DRILL BIT TO THE DRILL PIPE TO MAINTAIN A STIFF STEM ABOVE THE DRILL BIT FOR MINIMIZING DEVIATION OF THE DRILL BIT CAUSED BY CORKSCREWING OF THE DRILL PIPE UNDER LOAD, SAID DRILL COLLARS EACH INCLUDING AN ELONGATED BODY OF LESS CROSS SECTION THAN THE BORE HOLE MADE BY THE DRILL BIT, AND MEANS CONNECTING THE DRILL COLLARS IN END TO END RELATION WITH MAJOR PORTIONS OF THE DRILL COLLARS OFFSET OUTWARDLY FROM THE AXIS OF ROTATION AND WITH SAID MAJOR PORTION OF ONE DRILL COLLAR SPACED CIRCUMFERENTIALLY IN SYMMETRY WITH SAID MAJOR PORTION OF THE OTHER TO GYRATE IN CONTACT WITH THE WALL OF THE BORE HOLE. 